Approximately 50 species, including birds, mammals, reptiles, amphibians, fish, crustaceans and insects, are known to use the Earth's magnetic field for orientation and navigation. Birds in particular have been intensively studied, but the biophysical mechanisms that underlie the avian magnetic compass are still poorly understood. One proposal, based on magnetically sensitive free radical reactions, is gaining support despite the fact that no chemical reaction in vitro has been shown to respond to magnetic fields as weak as the Earth's ( approximately 50 muT) or to be sensitive to the direction of such a field. Here we use spectroscopic observation of a carotenoid-porphyrin-fullerene model system to demonstrate that the lifetime of a photochemically formed radical pair is changed by application of < or =50 microT magnetic fields, and to measure the anisotropic chemical response that is essential for its operation as a chemical compass sensor. These experiments establish the feasibility of chemical magnetoreception and give insight into the structural and dynamic design features required for optimal detection of the direction of the Earth's magnetic field.

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The magnetic properties of YVO3, a prototype of highly correlated d-electron Mott–Hubbard antiferromagnetic (AF) orthovanadates, are studied by means of magnetization and susceptibility measurements, coupled to 89Y NMR spectra and relaxation. Both field-cooled and zero-field-cooled conditions are considered. The history and field-dependent properties recently reported for the AF phases below TN≃113 K and TN′≃77 K are confirmed. The behavior in the paramagnetic phase and around TN is studied and it is shown how the field-induced short range order and canted-spin weak ferromagnetism is quenched in strong field, yielding (M/H)ZFC≃(M/H)FC for H≃6 T. At variance with the susceptibility in strong field, the 89Y NMR line width shows a divergent behavior for T→TN+. The 89Y relaxation rates do not display, for T→TN+, the behavior expected for spin fluctuations of AF-ferromagnetic (FE) symmetry as the one in the ordered state, possibly in view of the quasistatic character of the short range order.

Temperature-dependent ͑10-300 K͒ field-cooled ͑FC͒ and zero-field-cooled ͑ZFC͒ susceptibilities, and 89 Y NMR spectra and relaxation in Y 1Ϫx Ca x VO 3 with 0рxр0.9 are reported. In the paramagnetic phase ͑PA͒ of YVO 3 and for Tу120 K the susceptibility is of antiferromagnetic ͑AF͒ type, with no field dependence. Around the Neel temperature T N (1) ϭ113Ϯ1 K a field-dependent ferromagnetic behavior is observed under FC condition. Below T N(2) Ӎ77 K ͑AF phase with AF interplane coupling͒ strong difference is present between FC and ZFC 's. For T→T N (1)ϩ the 89 Y NMR line shows marked broadening and no measurable shift, consistent with a dominant dipolar contribution in the nucleus-electrons interaction. The 89 Y relaxation rate T 1 Ϫ1 , related to the correlated spin dynamics of V 3ϩ S(t), seems to indicate that the interplane ferromagnetic symmetry of the spin fluctuations is quenched in strong fields. The peculiar findings for and T 1 could result from a field-dependent weak ferromagnetism of Dzyaloshinsky-Moriya character. In Y 1Ϫx Ca x VO 3 , and T 1 Ϫ1 decrease on increasing x, still preserving the qualitative behavior as for xϭ0. For xӍ0.6 ͑Ca concentration which drives the transition to the metallic phase͒ the marks of the PA-AF transition are practically suppressed and behaviors characteristic of correlated metals are observed.

Abstraet. The motion of the flux lines (FL) in high temperature superconductors and their relationship with the NMR quantities are reviewed and discussed in the light of recent 89y NMR experiments in YBCO-type compounds. In particular measurements involving the 89y spin echo attenuation induced both by the thermal excitation of the FL's and by motions driven by DC current and pulsed magnetic fields are presented, with preliminary results and lines of interpretation. Flux line motion as observed with 199Hg NMR in HgBa2CuO4+ 6 high temperature superconductor is discussed.

The logistic regression model is a popular model for data analysis in epidemiological research. In this paper, we use this model to analyze genetic data collected from gene-longevity association studies. This new approach models the probability of observing one genotype as a function of the age of investigated individuals. Applying the model to genotype data on the TH and 3'ApoB-VNTR loci collected from an Italian centenarian study, we show how it can be used to model the different ways that genes affect survival, including sex- and age-specific influences. We highlight the advantages of this application over other available models. The application of the model to empirical data indicates that it is an efficient and easily applicable approach for determining the influences of genes on human longevity.

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